This invention relates to improvements in wear plates which are designed for convenient and removable installation in the pedestal opening of the side frame of a railway truck. More particularly, the invention relates to a clip-on pedestal wear plate of a known type which has an upwardly and downwardly facing surface and wherein the upper surface provides relatively higher friction than the lower surface to improve stability of the plate.
Clip-on pedestal wear plates are described in U.S. Pat. No. 3,897,736 and U.S. Pat. No. 4,203,371. The plate comprises a base adapted to cover and protect the downwardly facing surface of the pedestal opening. The plate includes a pair of lips joined to and extending upward from opposite sides of the base, said lips being resiliently engageable in clamped relation with opposite sides of the pedestal above the downwardly facing surface. The function of this type of wear plate is to prevent wear on the pedestal roof from a bearing adaptor, which is located over the axle bearing of the axle and wheel assembly of the truck. In the absence of a wear plate, limited movement or frictional sliding would occur directly between the arcuate top of the bearing adaptor and pedestal roof, causing worn spots on the roof, which is part of the side frame casting. The worn roof would have to be ground down and renewed by welding a plate in the opening, a time consuming and expensive procedure.
In most recent times, various proposals have been made to reduce the friction or absorb energy generated by engaging or load bearing parts in railway trucks, primarily to reduce wear or to improve performance characteristics. For example, the use of resilient shear pads are disclosed in U.S. Pat. Nos. 3,381,629, 3,638,582 and 4,363,278.
In addition, the use of low coefficient high density plastic liners at various locations in the railway truck have been proposed and placed in commercial use, for example, in U.S. Pat. Nos. 4,170,180 and 4,380,199. Polymeric liners, however, may be subject to abrasion when disposed against a rough steel part. Also, polymer liners are electrically non-conductive, and it is generally desirable to provide a conductive path from the rails and through the truck to the car body, in order to prevent build up of static electricity. Hence, if a non-conductive insert is employed in the pedestal roof, a separate conductive path would have to be provided.
In the manufacture and use of clip-on wear plates, it would be desirable to minimize movement of the wear plate relative to the side frame and to confine any movement to that between the wear plate and the bearing adaptor. Excessive movement of the wear plate itself causes high stresses in the lips and may lead to premature failure.